Combination anti-coronavirus therapies based on nonlinear mathematical models.

Using nonlinear mathematical models and experimental data from laboratory and clinical studies, we have designed new combination therapies against COVID-19.

Protein kinase C alpha protein expression is necessary for sustained erythropoietin production in human hepatocellular carcinoma (Hep3B) cells exposed to hypoxia.

Although protein kinase C (PKC) has been implicated as an effector of erythropoietin (EPO) production, its exact role is still uncertain. Hep3B human hepatocellular carcinoma cells were used for this study and were depleted of PKC in three different ways: long-term treatment with phorbol 12-myristate 13-acetate (PMA), selective inhibition with calphostin C, and treatment with PKCalpha antisense oligonucleotides. When EPO-producing Hep3B cells were incubated in 1% O2 (hypoxia) for 24 h, PMA treatment resulted in significant decreases in medium levels of EPO in Hep3B cell cultures at concentrations higher than 10 nM. The specific PKC inhibitor, calphostin C, significantly inhibited medium levels of EPO and EPO mRNA levels in Hep3B cells exposed to 1% O2. Western blot analysis revealed that Hep3B cells express the classical PKCalpha and gamma isoforms, as well as novel PKCepsilon and delta and the atypical zeta isoform. Preincubation with PMA for 6 h specifically down-regulated PKCalpha protein expression. Phosphorothioate modified antisense oligonucleotides specific for PKCalpha also decreased EPO production in Hep3B cells exposed to hypoxia for 20 h when compared to PKCalpha sense treatment. The translocation of PKCalpha from the soluble to particulate fractions was increased in Hep3B cells incubated under hypoxia compared with normoxia (21% O2) controls. These results suggest that the PKCalpha isoform plays an important role in sustaining hypoxia-regulated EPO production.

Post-transcriptional regulation of erythropoietin mRNA stability by erythropoietin mRNA-binding protein.

We have previously identified a sequence in the 3'-untranslated region (3'-UTR) of erythropoietin (Epo) mRNA which binds a protein(s), erythropoietin mRNA-binding protein (ERBP). A mutant lacking the ERBP binding site (EpoM) was generated. Hep3B cells were stably transfected with a wild-type Epo (EpoWT) cDNA or EpoM cDNA construct located downstream of a promoter of cytomegalovirus. Following inhibition of transcription, the half-lives of EpoWT and EpoM mRNAs were 7 h and 2.5 h in normoxia, respectively. The EpoM mRNA half-life remained unchanged in hypoxia. EpoWT mRNA half-life increased approximately 40% in response to a 6-h hypoxic pre-exposure and an additional approximately 50% when pre-exposed to 12 h hypoxia. The steady-state level of EpoWT mRNA was 4-fold that of EpoM mRNA reflecting the difference in mRNA decay rates in normoxia. The Epo protein level expressed from exogenous EpoM was unchanged in both normoxia and hypoxia. In contrast, the Epo protein level expressed from exogenous EpoWT increased 50% in hypoxia when compared with normoxia. These observations were further supported by chimeric chloramphenicol acetyltransferase and Epo-3'-UTR constructs. We have demonstrated that Epo mRNA stability was modulated in normoxia and further by hypoxia, therefore, providing evidence that Epo is regulated at the post-transcriptional level through ERBP complex formation.

Interaction of erythropoietin RNA binding protein with erythropoietin RNA requires an association with heat shock protein 70.

Synthesis of erythropoietin (Epo), the glycoprotein hormone that regulates red blood cell formation, is induced in response to low oxygen stress (hypoxia), and is regulated at both transcriptional and post-transcriptional levels. We have previously described an Epo RNA binding protein (ERBP) which specifically binds to the 3'-untranslated region of Epo mRNA and is likely involved in the regulation of Epo mRNA stability. Since heat shock proteins (hsps) are induced in response to a variety of stresses, including hypoxia, we tested the possibility that hsps are involved in ERBP-Epo RNA complex formation. When human anti-hsp70 antibody was added to ERBP-containing human hepatoma cell (Hep3B) lysates, the ERBP-Epo RNA complex was inhibited in an electrophoretic mobility band shift assay. In addition, the anti-hsp70 antibody-inhibited complex could be rescued if lysates were pretreated with purified inducible hsp70, but not with bovine serum albumin (BSA). In vivo studies using quercetin to inhibit hsp70 induction support the notion that hsp70 is involved in ERBP-Epo RNA complex formation. Taken together, these findings suggest involvement of hsp70 in ERBP-Epo mRNA complex formation, and our model suggests a novel role for hsps in the regulation of EPO mRNA stability.

Intracellular antibodies (intrabodies) for gene therapy of infectious diseases.

Intracellular antibodies (intrabodies) represent a new class of neutralizing molecules with a potential use in gene therapy. Intrabodies are engineered single-chain antibodies in which the variable domain of the heavy chain is joined to the variable domain of the light chain through a peptide linker, preserving the affinity of the parent antibody. Intrabodies are expressed inside cells and directed to different subcellular compartments where they can exert their function more effectively. The effects of intrabodies have been investigated using structural, regulatory, and enzymatic proteins of the human immunodeficiency virus (HIV-1) as targets. These intrabodies have demonstrated their versatility by controlling early as well as late events of the viral life cycle. In this article, we review studies of the use of intrabodies as research tools and therapeutic agents against HIV-1.

Changes in redox affect the activity of erythropoietin RNA binding protein.

We have previously identified a cytosolic protein, erythropoietin RNA binding protein (ERBP), which is up-regulated in certain tissues in response to hypoxia. To further characterize the interaction of ERBP and erythropoietin (EPO) mRNA, we have examined the role of reduction-oxidation in the EPO mRNA binding mechanism of ERBP isolated from human hepatoma cells (Hep3B). Reducing agents dithiothreitol (DTT) and 2-mercaptoethanol (2-ME) increased ERBP binding activity in a concentration-dependent manner, whereas the oxidizing agent, diamide, abolished ERBP binding activity. In addition, treatment of Hep3B cell lysates with the irreversible sulfhydryl alkylating agent N-ethylmaleimide resulted in inhibition of the EPO mRNA-ERBP complex. Taken together, these findings suggest that sulfhydryl groups may play a role in vivo in the regulation of EPO production through the modulation of ERBP binding activity.

Hypoxia up-regulates the activity of a novel erythropoietin mRNA binding protein.

The mechanisms which control the production of erythropoietin (Epo) remain enigmatic. Recent data suggest that the half-time of Epo messenger RNA (mRNA) is increased by hypoxia in Hep 3B cells, a human hepatoma line. The post-transcriptional regulation of other rapidly degraded mRNAs is mediated by sequence-specific mRNA binding proteins. In order to determine if Epo mRNA specific binding proteins exist, we probed cytosolic lysates from Hep 3B cells and mouse tissues with radiolabeled Epo RNA. A cytosolic protein that binds specifically to Epo RNA was identified in the Epo-producing, hepatoblastoma Hep 3B cell line by gel mobility shift assay. This protein was identified in both normoxic and hypoxic cells and bound specifically to a 120-base fragment of the 3'-untranslated region (3'-UTR) of Epo mRNA. Binding was completed with unlabeled Epo RNA, but not with granulocyte-macrophage colony-stimulating factor RNA. Ultraviolet light cross-linked Epo RNA-protein complexes migrated as two bands of 70 and 135-140 kD on sodium dodecyl sulfate-polyacrylamide gels. Binding activity was markedly increased in brain and spleen lysates from mice subjected to 24 h of hypoxia. Therefore, the post-transcriptional regulation of Epo expression in response to hypoxia may in part be due to the interaction of Epo RNA with its specific binding protein.

Increased secretion of erythropoietin in human renal carcinoma cells in response to atrial natriuretic factor.

The present studies were undertaken to assess the effects of atrial natriuretic factor (ANF) on erythropoietin (Ep) secretion in Ep-producing renal carcinoma (RC) cells using a sensitive radioimmunoassay for Ep. Human ANF produced a significant dose-related increase in Ep secretion at concentrations of 10(-7) and 10(-6) M when compared with vehicle controls. ANF (greater than or equal to 10(-9) M) also significantly increased the intracellular guanosine 3',5'-cyclic monophosphate (cGMP) concentration after 5-min incubation with the RC cells. Scatchard analysis of the human 125I-labeled ANF binding data indicated that the RC cells contain a single class of binding sites with a dissociation constant (Kd) of 93 +/- 1 pM and a binding capacity of 2,190 +/- 750 sites/cell. Incubation of the RC cells with 8-bromo-cGMP in concentrations of 10(-7)-10(-5) M also produced a significant dose-related enhancement of Ep secretion. These findings suggest that the increase in Ep secretion in response to ANF can be attributed, at least in part, to activation of guanylate cyclase, which is coupled to specific ANF receptors on the RC cell.

Effect of ATP and amiloride on ANF binding and stimulation of cyclic GMP accumulation in rat glomerular membranes.

We investigated ANF binding and stimulation of cGMP accumulation in isolated rat glomerular membranes in the presence and absence of amiloride and ATP. Amiloride enhanced high affinity binding of ANF without affecting its stimulation of cGMP. In contrast ATP decreased binding and decreased basal cGMP accumulation without affecting the ability of ANF to stimulate cGMP. These data indicate that ANF binding and stimulation of cGMP accumulation can be regulated independently supporting further the concept of receptor heterogeneity in renal glomerular membranes.

Association of the atrial natriuretic factor receptor with guanylate cyclase in solubilized rat glomerular membranes.

The elution profile of solubilized rat glomerular membranes from a gel filtration column showed two peaks of 125I-ANF (atrial natriuretic factor) binding (367 +/- 21, 156 +/- 12 KDa). Over 85% of the total binding for the extract was in the 367 KDa peak. Guanylate cyclase activity was correlated with 125I-ANF specific binding. ANF activation of guanylate cyclase was also observed. As observed previously with particulate membrane, Scatchard-analysis of ANF binding data with the solubilized extract was consistent with a two-site model. Both affinities (Kd's), 4 pM and 1 nM, are within the range of blood concentrations reported for ANF. These observations suggest that most rat glomerular ANF receptors are large molecular complexes coupled with guanylate cyclase in the 300-350 KDa size range.